1. Field of the Invention
The invention relates to the direct injection of fuel into internal combuston engines, in particular diesel motors.
2. Description of the Prior Art
It is known that to achieve complete combustion and desired power from diesel motors, injection must be carried out at a constant high pressure. To deal with this problem, there are already known injection devices of the pressure-time type featuring electromagnetic control, but these have certain drawbacks. Indeed, given the high injection rates called for by modern engines because of the high degree of supercharging for industrial vehicle motors or the high revolutions per minute for passenger car engines, the time allotted for injecting the amounts of fuel corresponding to a light load or a slow operating speed is quite short, and is on the same order of magnitude as the response time of the electromagnetic switches used to make the injector function.
To avoid this problem, there are known solutions involving the use of two electronic valves or servovalves for each injector, with one valve reserved for pressure control of the initiation of injection and the other valve serving to control the end of injection. These two control units execute the injection function perfectly but present other drawbacks. First of all, the injection nozzle is relatively bulky, making it difficult to install in the heads of the motor, especially in the case of passenger car engines. Second, the inevitable variance in response time results in irregularities between injection nozzles. Finally, the very design of the electromagnetic electrovalves or servovalves, which must have a rapid response time, inevitably causes leaks, not around the seats but as a result of cylinder-piston play, which have a major impact on the amount of fuel injected during the course of the same control period.
To avoid the latter problems, one known solution involves providing devices which amount to distributor-linked central hydraulic units in which the pressure control part of the injector (electroservovalves) is shared by several injectors, and the injection functions are distributed to the injection nozzles. While such a design ensures homogeneous operation by several injectors, it has, on the other hand, the drawback of giving rise to harmful hydraulic effects in the lines connecting the injection pressure control unit with the injector nozzles. In addition, given that there is a continuous high injection pressure around the injector needles, any improper functioning of the control unit poses a significant risk of flooding the engine, which justifies the addition of flow restriction units in the device.